Anode for primary cells and method for making same



Unite 2,726,279 Patented Dec. 6, 1955 ANODE FOR PRIMARY CELLS AND METHODFOR MAKING SAME Andr R. Gobat, North Caldwell, N. J., assignor toInternational Telephone and Telegraph Corporation, a corporation ofMaryland No Drawing. Application August 23, 1951, Serial No. 243,357

6 Claims. Cl. 136-120) This invention relates to the deferred type ofprimary cell which, when supplied with or immersed in electrolyte, isready for use, and more particularly to an anode for such cells.

Dry primary cells of the deferred type have been proposed heretofore forstorage in the dry state and operative by addition of a suitableelectrolyte. In such cells, an anode of magnesium can be used. Themagnesium anode, however, tends to deteriorate during storage because ofits high reactive characteristic. When such cells are stored, the anode,unless kept exceptionally dry such as in a dehumidified atmosphere,tends to corrode in reaction with the moist atmosphere and certain saltsordinarily included in the cell assembly. This corrosion of the anode,of course, reduces the eifective life of the cell and is one of the maindifliculties encountered with the deferred type of primary cell. Efforthas been made heretofore to overcome this deterioration of the magnesiumanode, but with only little success. It has been proposed, for example,to treat the anode with a dilute aqueous solution of chromic acid oralkali metal chromate or dichromate, after which it is dried andincluded in the cellassembly. Such treatment, however, tends to depressthe activity of the anode during service operation, thus reducing thevoltage and current output of the cell. Furthermore, such treatment isonly partially effective in inhibiting the anode corrosion in thepresence of moist atmosphere.

One of the objects of this invention is to provide an improved magnesiumanode for the deferred type of primary cell which has a high resistanceto moist atmospheres and which resists deterioration during longstorage.

Another object of the invention is to provide a magnesium anode for usein a primary cell with a coating having a catalytic eifect on theactivity of the anode when supplied with electrolyte in a cell assemblyand yet which inhibits activity of the anode while stored in cellassemblies, even though in the presence of moist atmosphere; and afurther object is to provide a method of applying such coating.

One of the features of the invention is the particular protectivecoating, and another is the method by which the coating is formed on thesurface of the magnesium anode. A strip of magnesium is selected ofdesired size and shape depending on the type of cell to be made, whetherof the flat electrode type or coiled electrode form, and preferably ofthin foil thickness. The magnesium strip is then prepared in accordancewith the principles of this invention as follows:

(1) The magnesium strip is cleaned and degreased by any suitable methodsuch as by immersion in a hot bath of trichloroethylene obtainable as acommercial solvent known as Tri-clean.

(2) The magnesium strip, depending upon the type of cell to be formed,may be specially formed at this stage of the preparation. The specialshaping, such as making the foil strip corrugated or ridged, relievesthe foil of certain strains and renders it uniform in the shape desired.

Corrugations are also sometimes desirable to increase the active surfaceof the anode for a given area and to enable rapid access of electrolyteto the surfaces of electrodes and for the escape of gases.

(3) Where the magnesium anode has been subjected to a special shapingoperation following the cleaning and degreasing step, it is preferableto again clean the magnesium strip by subjecting it to an etching bathwhich may comprise, for example, a bath of acetic acid and sodiumnitrate, after which the strip is washed with water for about 30seconds.

(4) The magnesium strip is next subjected to a bath of mercuric saltsand acetic acid, whereby it becomes coated with magnesium amalgam. Anysoluble mercuric salt may be used, convenient salts for this preparationbeing mercuric acetate and mercuric nitrate. The proportions of the bathare not critical. Where mercuric acetate is used, for example, theproportions may be in the amount between 5 and 100 grams of mercuricacetate per liter of solution and the acetic acid may be in the amountof 2 /2 to 200 milliliters of acetic acid per liter of solution. Theonly pre-requisite is to provide suflicient mercuric ions in solution toeffect a thin coating on the magnesium foil. By way of example asatisfactory ratio of these two ingredients used in practicing theinvention is 30 grams mercuric acetate per liter of solution and 15milliliters acetic acid per liter of solution. The immersion of theanode in this bath may be for a short period of about 10 seconds at roomtemperature, the period being varied according to the bath concentrationand temperature.

(5) The treated magnesium strip is next washed in water for about 30seconds to remove traces of the soluble salts.

(6) In order to maintain the magnesium amalgam coating on the magnesiumstrip and protect it against moist atmosphere, the strip is nextsubjected to a bath of potassium dichromate for about 60 seconds at roomtemperature using in the neighborhood of 50 grams of potassiumdichromate per liter of solution. The strength of this bath may bevaried considerably depending upon the period of immersion andtemperature. This bath acts as a fixing bath and in eflfect appears toprovide a protective coating over the magnesium amalgam which protectsit from moist atmosphere, but which when wetted by a suitableelectrolyte permits immediate reaction.

(7) After the fixing bath the magnesium strip is again washed withwater, this time for about 20 seconds.

(8) The strip is removed from the washing operation and dipped through abath of acetone to enhance rapid drying and is then dried.

From the foregoing description it will be clear that the treatment ofthe magnesium anode serves two purposes: one, to provide it with acoating of magnesium amalgam, and second, to protect the magnesiumamalgam coating from deterioration. The amalgamated magnesium surfaceWhen supplied with an electrolyte appears to have a catalytic actionwhich provides a higher voltage for the cell assembly than obtainedheretofore with magnesium anodes.

For an example of a cell assembly incorporating a magnesium anodetreated according to the principles of this invention, reference may behad to the copending application of A. 1. Warner and A. R. Gobat issuedas U. S. Patent No. 2,661,388, December 1, 1953. In such cell thecathode is provided with a silver chloride compound and is disposed inclose, spaced relation with respect to the amalgamated magnesium anodewith a suitable porous electrical insulating material therebetween. Foreight-cell batteries of the silver chloride-magnesium deferred actiontype, heretofore provided, the best voltage obtainable was about 11.3volts for a discharge current 3 of approximately 1.5. amperes per squaredecirneter of electrode surface. With eight-cell batteries made inaccordance with the present invention, as more particularly set forth insaid copending application, a V0 tage of 12.3

volts was consistently obtained for discharge currents of nearly 2amperes per square decimeter of electrode surface. The initial voltagerise, after immersion in water, was much quicker for batteries madeaccording to the present invention than for the older type, and the timeintegral of the voltage, for voltages in excess of 1 volt per cell, wasmuch improved. An individual silver chloride-magnesium cell, forinstance, incorporating a magnesium anode treated in accordance withthis invention showed the following discharge characteristic. Whentested against a fixed discharge conductance of 0.14 mhos per squaredecimeter electrode surface, the voltage across the dischargeconductance rose to one volt within less than 10 seconds. At the end ofone minute the voltage exceeded 1.5 volts and the current was greaterthan 2 ampercs per square decimeter electrode surface. The duration ofthe cells continuous operating service at a voltage exceeding 1 volt waswell over nine minutes.

Besides using the specially treated magnesium anode with a silverchloride cathode, cathodes of many other materials may be used. Anydepolarizing material, such as lead dioxide, manganese dioxide, nickeldioxide, copper chloride, silver oxide, and silver peroxide, may be usedin a cell assembly with the magnesium anode treated in accordance withthe present invention.

While I have described above the principles of my invention inconnection with specific apparatus, it is to be clearly understood thatthis description is made by way of example only and not as a limitationto the scope of my invention as set forth in the objects thereof and inthe accompanying claims.

I claim:

1. In a deferred-action primary cell activated by being wetted byelectrolyte, an anode comprising magnesium having a layer of magnesiumamalgam and a chromated coating thereon protecting said layer fromdeterioration prior to activation of said cell.

2. The. method of improving the resistance to corrosion in a moistatmosphere and the electrode activity when supplied with electrolyte ofa magnesium anode for a deferred-action primary cell comprising cleaninga strip of magnesium, subjecting the clean magnesium strip to a bathcontaining a soluble mercuric salt to provide a layer of magnesiumamalgam on the surface of said strip and subjecting said layer to achromating treatment, thereby rendering it inactive in the presence ofmoist atmosphere.

3. A method according to claim 2, wherein the mercuric bath includesmercuric acetate and acetic acid.

4. A method according to claim 2, wherein the mercuric bath includesmercuric nitrate and acetic acid.

5. A method according to claim 2, wherein the treatment of the magnesiumstrip includes washing the strip after forming the layer of magnesiumamalgam and wherein said layer is chromated by subjecting the strip to abath of potassium dichromate.

6. The method of improving the resistance to corrosion in a moistatmosphere and the electrode activity when supplied with electrolyte ofa magnesium anode for a deferred-action primary cell comprising etchinga strip of magnesium, subjecting the etched strip to a bath including asoluble mercuric salt and acetic acid to form a layer of magnesiumamalgam on the surface of the strip, subjecting the strip to a bath ofpotassium dichromate, washing said strip and drying the strip.

References Cited in the file of this patent UNITED STATES PATENTS 741Elkington May 17, 1838 1,696,873 Wood Dec. 25, 1928 1,771,190 PolcichJuly 22, 1930 1,783,770 Beck et al. Dec. 2, 1930 2,143,959 SchumpeltJan. 17, 1939 2,454,799 Hart et al. Nov. 30, 1948 2,553,449 Freud May15, 1951 FOREIGN PATENTS 1,789 Great Britain of 1853

1. IN A DEFERRED-ACTION PRIMARY CELL ACTIVATED BY BEING WETTED BYELECTROLYTE, AN ANODE COMPRISING MAGNESIUM HAVING A LAYER OF MAGNESIUMAMALGAM AND A CHROMATED COATING THEREON PROTECTING SAID LAYER FROMDETERIORATION PRIOR TO ACTIVATION OF SAID CELL.
 2. THE METHOD OFIMPROVING THE RESISTANCE OF CORROSION IN A MOIST ATMOSPHERE AND THEELECTRODE ACTIVITY WHEN SUPPLIED WITH ELECTROLYTE OF A MAGNESIUM ANODEFOR A DEFERRED-ACTION PRIMARY CELL COMPRISING CLEANING A STRIP OFMAGNESIUM, SUBJECTING THE CLEAN MAGNESIUM STRIP TO A BATH CONTAINING ASOLUBLE MERCURIC SALT TO PROVIDE A LAYER OF MAGNESIUM AMALGAM ON THESURFACE OF SAID STRIP AND SUBJECTING SAID LAYER TO A CHROMATINGTREATMENT, THEREBY RENDERING IT INACTIVE IN THE PRESENCE OF MOISTATMOSPHERE.